1. Field of the Invention
The present invention relates to a method and apparatus for cutting a cover thread of a multi-needle sewing machine which uses a cover thread.
2. Description of the Related Art
A device for automatically cutting the cover thread afler the needle thread seam at the end of sewing, is known.
Among the known devices, as disclosed in Japanese Laid-open Patent Sho. 57-128195, Utility Model Sho. 58-177086, Patent Sho. 59-55286, and Utility Model Sho. 60-179282, at the end of sewing, when the needle and feed dog reach the top end point and the curved cover thread layer finger stops at the left dead center, the cover thread, extending from the right needle thread seam at the end of sewing to the hook of the curved cover thread laying finger, is captured and cut by the hook of the thread cutter, which reciprocates at an oblique angle from the left rear side of the left needle or the right operator side of the left needle. The cut end of the cover thread at the cut-off thread supply source side is directly clamped in the thread cutter, and is caught by a specified needle or captured by the curved cover thread laying finger when starting the next sewing work, so as to be securely sewn into the first needle thread seam. As disclosed in the Japanese Laid-open Patent Sho. 61-45796, at the end of sewing, when the needle and feed dog stop at the bottom end point and the finger stops at the right end point, the cover thread, extending from the right needle thread seam at the end of sewing into the cover thread guide above the finger, is captured and cut by the hook of the thread cutter which reciprocates at an oblique angle from the right rear side of the right needle. The cut end of the cover thread is directly clamped in the thread cutter, so as to be captured by the finger when starting the next sewing work.
In all these conventional machines, however, since the cover thread is designed to be captured as the hook of the thread cutter advances into the space between the top surface of the presser foot and the curved cover thread laying finger, the spacing between the top surface of the presser foot and the curved cover thread laying finger becomes narrow in the case of a thick fabric, so that the hook of the thread cutter may not get in easily.
These conventional thread cutters are composed of a fixed cutter, a hook of the thread cutter which moves in and out sliding on the fixed cutter, and a leaf spring for pressing the hook to the fixed cutter. The cover thread, captured by the hook, is pulled to the fixed cutter and is cut off by the cutter, and the cut end of the cover thread at the cut-off thread supply source side is pinched and held by and between the hook and the leaf spring. In such devices, however, although it is advantageous that the hook is tightly pressed to the fixed cutter by intensifying the spring pressure of the leaf spring to cut the thread securely, the holding force on the cut thread end increases, and the thread end may not easily slip off from the hook and leaf spring when starting the next sewing work, which may lead to uneven pulling of the cloth or breakage of the needle.
Although it is not a thread cutter for a cover thread, a device having a leaf spring for holding the thread end by lightly and elastically contacting with the hook for the thread cutter, and a leaf spring for pressing the hook to the fixed cutter, is known. An example of this type is shown in the Japanese Utility Model Publication Sho. 63-10149. According to this device, the thread may be securely cut off by properly adjusting the spring pressures of individual springs, and the cut thread end may be lightly held with the minimum pressing pressure required. However, since the leaf spring is of the cantilever type, and its free end is pressed to the hook of the thread cutter, the leaf spring must be long enough to lightly and elastically contact with the hook of the thread cutter when the leaf spring is holding the thread end, and the design is not compact. In this type, the contact area with the hook is small and the holding force is lowered, so that the thread end holding is unstable, and it is always necessary to adjust the spring force.